In rechargeable secondary batteries used for many kinds of electronic devices, miniaturization and weight saving of the battery have been called for with progress in the electronic devices, such as a cellular phone and a personal computer. A rechargeable lithium-ion battery is represented as the rechargeable battery with high energy density which can meet this demand. On the other hand, the rechargeable batteries, such as a lead storage battery and a nickel-hydride battery are used as the large capacity power supply source for the electronic devices represented by an electro-mobile, a hybrid car, an electric motorbike, and a forklift, etc. However, these days, development toward adoption of the rechargeable lithium-ion battery with high energy density has been advanced actively. In order to respond to it, the development of the rechargeable lithium-ion battery is focused on long life and safety to achieve bigger size and larger capacity.
Large driving electric power is needed as power supply sources of above electronic devices when using the rechargeable lithium-ion battery. Accordingly, a battery pack which accommodates many batteries connected in series or in parallel is used.
Amount of current outputted from each battery becomes large with progress of the largess in size and output capacity. Accordingly, in order to suppress the Joule heat of the external electrode terminal, it is necessary to make a resistance of the external electrode small, which results in indispensable enlargement of the external terminal.
Moreover, the battery external terminals of some batteries are connected in series or parallel by external leads. Therefore, stress may be directly applied to the external leads, which may result in a rotation of the cathode terminal or an anode terminal, and further an external short circuit due to the rotation.
Japanese Patent Application Laid Open Nos. (1) P2003-45403, (2) P2003-115287, (3) P2003-151528, and (4) P2000-113865 disclose batteries in which the external electrode terminal like a positive electrode terminal are fixed to a lid by caulking of a gasket consisting of two portions.
Recently, in order to maintain a high air-tightness even in the operation under high temperature, expensive tetrafluoroetylene-perfluoroalkoxyetylenevinyl-ether copolymers (PFA) of fluoride resin is used for the material of the gasket more often (for example, laid open patent applications (1)-(3)). The gasket becomes large with increase in the external electrode terminal, and the amount of the resin which is used therein increases, which results in a problem of raising the cost of the gasket.
Furthermore, PFA is rather soft among the resin materials, therefore, if the external terminals rotate, the gasket may be destroyed. Consequently, if a head portion of the external terminal contacts with the lid, a risk of a short circuit is accompanied.